The present invention relates to decorative coatings for plastic substrates, the decorative coatings ideally being stable and durable coatings that are spectrally tunable to permit the selection of a variety of appearances, including chrome tints, from a gun-metal grey to a piano black, or a brushed-metal look, ideally to provide a decorative metal finish. While the primary use for the coatings of the present invention will generally be as decorative metal finishes in the areas of automotive trim (interior and exterior), consumer goods (such as whitegoods) and various electrical products (such as switch housings), it will be appreciated that the invention is not to be limited to only those uses.
Decorative coatings, especially decorative metal finishes, are becoming increasingly desirable as designer surfaces on a variety of consumer goods including premium automotive interior and exterior trim components, consumer and household goods, as well as fashionable household electronic products, and either as partial or full surfaces for those goods. Furthermore, chrome finishes with custom colours and tints (often with a “brushed-metal” look) are becoming increasing desirable. Such coatings include tinted and deep dark chromes, as well as satin finishes.
While bulk metal can be used for such applications, it is not only heavy and cumbersome to work with, but also difficult and expensive to machine and polish into the complex shapes that are common across these types of components. In addition, bulk metal does not support ‘surprise and delight’ hidden lighting, or back lighting in general, nor does it lend itself to the formation of a surface where a part of the surface has a different appearance to another part of the surface. Thus, it tends to be more desirable to utilise plastic substrates in such cases.
While metal-look paints, film laminates and metallic inks offer options to create chrome-look surfaces on plastic substrates, they lack the authentic metal appearance that is required with these types of finishes and often show poor durability.
Electroplating of plastics is a common process in depositing metals such as copper, nickel and chrome onto plastic surfaces to create high quality finishes. While these coatings offer high durability, they tend to be susceptible to issues with corrosion (Na, Mg or Ca salts) and electroplating itself utilises hazardous substances (such as Cr6+) that are not environmentally sustainable. Furthermore, they lack the flexibility to cover all areas of the colour spectrum to offer wide customisation of colour tunability and depth of black on chrome. For example, electroplaters offer tinted chromes that not only offer limited durability and colour fastness but are limited to specific areas of the colour spectrum, typically in the positive a* and b* colour space (in the CIELAB system) which is yellow in appearance.
Also, electroplating is completely opaque and does not support ‘surprise and delight’ hidden lighting, or back lighting in general. In addition to metal finishes, back lighting is becoming a unique branding method for designers to create new functionality with surfaces, increasing the value of their product and further differentiating them from their competitors. Examples of branded back lighting include hidden icons or displays behind tinted plastic or film, and backlighting of fabrics and graphics to create a “surprise and delight’ for the consumer.
Physical vapour deposition (PVD) of metals onto plastic surfaces is also a common method of applying metal coatings to plastic surfaces to create a metallic-look finish and can be created thin enough to allow light transmission. However, such coatings are not physically and environmentally durable enough to survive even the most basic consumer testing requirements.
Indeed, none of the above metallic coatings possess tunable properties to offer durable, decorative finishes that allow light transmission. No such coatings offer the ability to converge the need for spectral and optical tunability with metallic finishes to create functional, highly durable, customisable chrome surfaces (for example) from bright through to deep black colours with backlighting functionality if desired.
There is thus a need for a durable, spectrally tunable surface for plastic substrates that allows for the selection of broad ranges of appearance, such as high intensity blacks, and that can be substantially transparent so as to permit hidden lighting functionality if desired.
The above discussion of background is included to explain the context of the present invention. It is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge at the priority date of any one of the claims.